I cook mine fat side down.
Here's why: I cook on a Stumps Smoker and the heat source is at the bottom of the pit. And yes, the fat does help keep the bottom from drying out (I've tried fat up vs. fat down several times). If using a stick burner, I don't think it would make that much of a difference. The air flow in an off-set (a good one) pit allows the air to flow above and below the meat. The cooker I cook on works in a different way which can dry out the bottom of the meat.
I think what you're cooking on makes a huge difference.